Electric initiator and ignition mixture therefor



Sept. 4, 1956 D. T. ZEBREE 2,761,335

ELECTRIC INITIATOR AND IGNITION MIXTURE THEREFOR Filed Dec. 3, 1952DAVID T. ZEBREE INVENTOR.

BY W (21mm ELECTRIC INITIATOR AND IGNITION MIXTURE THEREFOR David T.Zebree, Kingston, N. Y., assignor to Hercules Powder Company,Wilmington, DeL, a corporation of Delaware Application December 3, 1952,Serial No. 323,866

13 Claims. (Cl. 102-48) This invention relates to blasting initiatorsand more particularly to ignition compositions and initiators employingsuch compositions.

For many years mixtures of finely divided lead and selenium have beenemployed in the electric initiator art with very satisfactory results.As the initiator art developed, it became apparent, however, that thisgenerally satisfactory composition was characterized by certaindeficiencies which it has been desirable to correct. For example, it hasbeen discovered that failures in regular delay blasting initiatorsresulting from the oxidation of lead in the lead-selenium mixture couldbe overcome by the addition to the mixture of certain amounts ofaluminum, antimony, antimony phosphide, boron, cadmium, carbon, iron,magnesium, nickel, phosphorus, and silicon. These improved mixtures aredisclosed in copending application Serial No. 78,383, filed February 25,1949.

Although the addition of such modifiers was found to eliminateoverlapping of delay periods in regular delays, that is, delayinitiators in which the period between application of current and thefiring of the cap is measured in terms of a second or more, thelead-selenium mixtures and the modified lead-selenium mixtures ofapplication Serial No. 78,383 are still characterized by an undesirablelack of uniformity in firing time when employed in short period delaycaps wherein the period of delay is measured in terms of milliseconds.

While lead-selenium ignition compositions are generally characterized bysatisfactory resistance to premature firing by static discharge, itwould, of course, be desirable to increase this resistance to staticdischarge if such increase can be effected without adversely alfectingthe otherwise acceptable performance of the mixture. In like manner, itwould be desirable to improve the charging characteristics of alead-selenium mixture since such mixtures are normally quite dusty. Asin the case of any ignition composition which is employed with highexplosive materials, it is desirable to increase the impact sensitivityof the mixture in so far as it is possible Patented Sept. 4, 1956without adversely affecting the ignition characteristics of thecomposition.

Now in accordance with the present invention, compositions predominantlycomprising mixtures of lead and selenium can be prepared which haveincreased resistance to ignition by static discharge, which have betterflowing and charging characteristics, which have lower impactsensitivity, and which, when employed in short period delay initiators,bring about considerably greater uniformity in firing time.

Generally described, the present invention is an ignition compositionfor electric initiators which comprises lead-selenium and a minor amountof a metal salt of a long chain fatty acid. It has been found that thepresence of a suitable amount of such metallic soaps in mixturepredominantly comprising lead and selenium efiects highly desirablechanges in terms of uniformity of firing time, particularly in shortperiod delay initiators, static resistance, charging ease, and frictionand impact sensitivity without detracting from the other widely acceptedcharacteristics of lead-selenium mixtures. While the metal salts of thelong chain fatty acids are generally operable, the stearates, oleates,laurates, and palmitates of such metals as lead, cadmium, iron,magnesium, aluminum, and zinc are most readily available and arepreferred. Of all of these compounds lead stearate is especiallypreferred. While the mixtures of this invention are especially adaptedfor usein short period delay initiators, they may be used as well ininstantaneous and regular delay initiators.

The eifect of the presence of metallic soaps in leadselenium onuniformity of firing times of short period delay caps is shown in TableI. The caps employed are illustrated in the drawing and comprise abronze shell 1 containing a pressed base charge 2 of 0.24 g. ofpentaerythritol tetranitrate. A priming charge 3 of 0.38 g. ofdiazodinitrophenol/potassium chlorate (75/25) was pressed on top of thebase charge. A delay fuse consisting of a load tube 4 containing a core5 of barium peroxide/selenium (/30) is pressed on the priming charge. Aloose charge 6 of ignition composition in accordance with the inventionis loaded on top of the fuse. An ignition plug 7 is inserted over theignition composition. Lead Wires 8 pass through the ignition plug intothe ignition composition and are connected at their terminals by abridge wire 9 which is surrounded by the ignition composition. A layerof waterproofing 10 and a sulfur seal 11 complete the initiator.

In the test recorded in Table I, the indicated number of caps wasseparately fired and the elapsed time (measured in milliseconds) betweenapplication of the firing current and the firing of the cap was measuredfor each. A firing current of 2 amperes was employed. Unless otherwiseindicated, a chemically equivalent mixture of lead and selenium wasemployed (Pb-Se72.4/ 27.6).

Table II Example N o. Ignition Mixture Condens- M.N'.F.

er (mmf.) V.

Pb-Se/Si, 98/2 100 4, 000 Pb-Se/Si, 98/2 750 1, 000 Pb-Se/Si, 98/2 3,0001,000 Pb-Se (alone) 750 1, 000 Ph-Se/lead stearate, 99. 100 6,000Pb-Se/lead stearate, 99.5/0.5 750 2, 000 Pb-Se/lead stearate, 99.15/05.3, 000 1, 000 Pb-Se/Si/lead stearate, 97.5/2.0/0.5 100 6, 000Pb-Se/Si/lead stearate, 97.5/2.0/0.5 760 2, 000 Pb-Se/S1/lead stearate,97.5 2 /0 3, 000 1,000 Pb-Se/slllead stea. ate, 97 5/1 0/1 5 750 2, 000Pb-Se/Sr/lead stearate, 97. [1.0/2 0- 750 3, 000 Pb-Se/Si/lead stearate,96.5/1.0/2.5 750 4, 000 Pb-Se/Si/calcium stearate, 97.5/l.0/1.5 750 3,000 Pb-Se/S1/iron stearate, 97. 5/1.0/1 .5 750 2, 000Pb-Se/Si/rnagnesium stearate, 97.5/1 .0/1.5 750 3, 000 Pb-Se/Si/zincstearate, 97.5/1.0/l.5 750 3, 000 Pb-Se/Si/aluminum laurate,97.0/l.0/2.0 750 2, 000 Pb-Se/Si/calcium oleate, 96.0/1.0/3.0 750 2, 000

1 Maximum nonfiring voltage.

The diminution 1n lmpact and friction sensitivity ef- 78,3 83. Theamount of metal salt wh1ch can be added fected by addition of the metalsoaps is illustrated in Table III. In the experiments recorded, thecompositions were tested on a Bureau of Mines impact machine todetermine the height and angle necessary to give 50% shots.

to a lead-selenium mixture without desensitizing the composition toignition will depend on the amount of such other additive employed andon the firing current used. With a firing current of 2 amperes and abasic stoichiometric mixture of lead and selenium containing 1% of TableIII Example Weight, Impact Height for 50% N o. Ignition Mixture Kg.A(rg)gle Shots (cm.)

Pb-Se(72.4-27.6)/Sl, 98/2 2 4 16. Pb-Se(72.4-27.6)/Si, 98/2 4 8 11.Pb-Se(72.427.6)/Sillead stearate, 97. 2 4 41. Pb-Se(72.4-27.6)/Si/leadstearate, 96.5/2.0 1. 4 4 48. Pb-Se(72.427.6)/Si/lead stearate,96.512.0/1. 4 8 5O shots. Pb-Se(72.427.6)/Si/lead stearate, 96.0/2.0/2.04 4 7% shots.

1 Maximum height of test machine; hence, height of fall for 50% shotswas over 50 cm.

From the foregoing examples it is apparent that the compositions andinitiators of this invention are characterized by highly desirableproperties. From the examples in Table I, it will be noted that with afiring current of 2 amperes, failures are obtained when enough metalsoap is employed to reduce the ignition sensitivity of the mixture. Aswill be apparent to those skilled in the art, the concentration at whichundesirable ignition sensitivity will be obtained depends on thestrength of the firing current employed and on the amount of silicon orother ignition desensitizing additive employed. When employing a firingcurrent of 2 amperes, for example, it has been found that up to 6% oflead stearate may be added to a chemically equivalent lead-seleniummixture without undesirably desensitizing the composition to ignitionalthough between .5 and 2% is preferred. A definite benefit was notedwhen .2% lead stearate was added.

In order to guard against failures due to formation of lead oxide in themixture, it is desirable to add silicon or other additive in accordancewith application Serial No.

silicon, it has been found that the following amounts of metal soapswill desirably be added:

Preferred ignition mixtures in accordance with the invention willcontain from about 64 to about lead, from about 20 to about 36%selenium, from about .2 to about 2% silicon, and from about 0.5 to about2% lead stearate.

With respect to static resistance and impact and friction sensitivity,Tables II and III illustrate that the benefits received increased inproportion to the amount of additive employed. Since the metal soap hasa lubricating efl'ect on the powdered lead-selenium mixture, the fiowingand charging characteristics of the mixture are markedly improved.

Since various modifications of the invention not specifically set forthherein will occur to those skilled in the. initiator art, it is intendedthat the scope of the invention be limited only by the scope of theappended claims.

What I claim and desire to protect by Letters Patent is:

1. An ignition composition for electric initiators which comprises anignition mixture of lead and selenium and contains a minor amount ofmetal salt of a long chain fatty acid.

2. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, and aminor amount of metal salt of a long chain fatty acid.

3. An ignition composition for electric initiators which comprises astoichiometric mixture of lead and selenium and a minor amount of metalsalt of a long chain fatty acid.

4. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, and aminor amount of metal salt of stearic acid.

5. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, and aminor amount of metal salt of lauric acid.

6. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, and aminor amount of metal salt of oleic acid.

7. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, and aminor amount of lead stearate.

8. An ignition composition for electric initiators which comprises fromabout 64 to about 80% lead, from about 20 to about 36% selenium, andadditive amounts of from about .2 to about 2% silicon, and from about .5to about 2.0% of lead stearate.

9. An electric blasting initiator having in combination an ignitionassembly containing a bridge wire and a loose ignition mixture disposedabout the bridge wire which comprises an ignition mixture of lead andselenium and contains a minor amount of metal salt of a long chain fattyacid.

10. An electric blasting initiator having in combination an ignitionassembly containing a bridge wire and a loose ignition mixture disposedabout the bridge wire which comprises from about 64 to about lead, fromabout 20 to about 36% selenium, and a minor amount of metal salt of along chain fatty acid.

11. An electric blasting initiator having in combination an ignitionassembly containing a bridge wire and a loose ignition mixture disposedabout the bridge wire which comprises from about 64 to about 80% lead,from about 20 to about 36% selenium, and additive amounts of from about.2 to. about 2% silicon, and from about .5 to about 2.0% of leadstearate.

1.2. A delay electricblasting initiator having in combination a delayfuse element and a loose ignition mixture in contact with the delay fuseelement; said mixture comprising from about 64 to about 80% lead, fromabout 20 to about 36% selenium, and a minor amount of metal salt of along chain fatty acid.

13. A delay electric blasting initiator having in combination a delayfuseelement and a loose ignition mixture in contact with the delay fuseelement; said mixture comprising from about 64 to about 80% lead, fromabout 20 to about 36% selenium, and additive amounts of from about .2 toabout 2% silicon, and from about .5 to about 2.0% lead stearate.

References Cited in the file of this patent UNITED STATES PATENTS1,989,729 Alexander Feb. 5, 1935 2,473,405 Zebree June 14, 19492,476,370 I-lanley July 19, 1949 2,607,672 Spaeth et al. Aug. 19, 1952FOREIGN PATENTS 114,993 Australia Mar. 7, 1946

9. AN ELECTRIC BLASTING INITATOR HAVING AN COMBINATION AN IGNITIONASSEMBLY CONTAINING A BRIDGE WIRE AND A LOOSE IGNITION MIXTURE DISPOSEDABOUT THE BRIDGE WIRE WHICH COMPRISES AN IGNITION MIXTURE OF LEAD ANDSELENIUM AND CONTAINS A MINOR AMOUNT OF METAL SALT OF A LONG CHAIN FATTYACID.